Lowitz
oriented plates or columns take rotational positions - they don’t necessarily
spin - about a near horizontal Lowitz axis ‘AA’. The
axis passes through two opposite prism edges and is parallel to
the hexagonal end faces.

The orientation and its halo
arcs are named after Tobias Lowitz
who first reported them in 1790.
Their existence was long doubted but the halos are now occasionally
observed and digitally photographed although clear examples remain
very rare.

Crystals with the classic Lowitz orientation
take all positions
about the axis LL. In practice, the crystals may have a
more restricted range of angular positions.

Rays can pass through two side faces with
a wedge angle of 60° in
three ways to form upper, middle and lower Lowitz
arcs. Rays
internally reflected from end faces form reflected Lowitz arcs,
long pillar like extensions from the parhelia when the sun is
very low.